The present invention relates to non-destructive testing apparatus and, more particularly, to a novel energy reflection flaw detection system having high resolution and stability to facilitate removal or controlled attenuation of undesirable echoes from surfaces of the object of be analyzed and facilitating analysis of flaws closely adjacent to those surfaces, as well as throughout the volume of the object-under-test.
Known energy reflection flaw detection systems, such as conventional immersion ultrasonic flaw detectors, generally require improvement in timing accuracy, resolution and stability to provide the maximum meaningful data obtainable. In particular, flaws located near the surfaces of an object-under-test are often undiscernable, due to the reflection of energy from edges and surfaces of the object returning from the object at substantially the same time as the reflections from the flaw to be investigated, which flaw reflection is generally of lesser amplitude than the surface and/or edge reflection. Means for removing the surface reflections in highly stable and consistent fashion are therefore desirable. Similarly, a problem exists in that the beam of energy interrogating the object-under-test is often focussed at a point in the object, whereby the beam power density increases as the focal point in approached and then decreases thereafter, generating varying reflection amplitudes for equal magnitude flaws at different positions within the object, which (when combined with varying amplitude from a single flaw due to the non-uniformness thereof) often result in the largest flaws being ignored by the detection system in favor of relatively smaller flaws having a boundary surface disposed in such manner as to reflect somewhat greater energy in a greater power density portion of the beam. Therefore, means for offsetting the varying power density of the beam and means responsive to small portions of a reflected signal are desirable to alleviate this problem.